Optimized cy_expect_rho_vec

Here we calculate only what is required.
Update spmatfuncs.c
Now cy_expect_rho_vec calls cy_expect_rho_vec_fast
Update spmatfuncs.c
Rename to cy_expect_rho_vec_csr
Update spmatfuncs.c
Merge pull request #56 from Vutshi/patch-7

Add fast cy_expect_rho_vec